The circuits and devices needed for electrical or electronic systems are usually located inside cubicles that perform the double function of support and protection. The cubicles in question must provide mechanical sturdiness, since for safety reasons, they are usually required to be able to stand relevant stresses, including bursts or explosions, which might occur in electric energy distribution systems owing to possible short-circuits.
To comply with the mechanical sturdiness requirement, such cubicles are usually in the form of a metallic structure which is covered with panels anchored with the structure itself.
Considering that such cubicles may present a wide range of sizes, the metallic structure is usually obtained by assembling a plurality of elementary pieces from bars and iron sheets.
The assembly means usually consist of a joint which, for reasons of weight and ease of working, is usually realized in die-cast aluminum.
In fact, aluminum provides such a specific gravity as to allow to contain the weight of the joints and consequently of the structure in its whole and may be easily worked by die-casting.
According to known structures the connection of joints with the bar portions is realized by way of screws whose head is inserted into recesses provided in the bars and whose shank results screwed on threaded holes obtained in the body of the joint. In particular, the bars usually provide a polygonal section and each bar portion is linked to the joint by way of two screws located at diametrically opposite points of the said polygonal section.
Thus a fair distribution of the prestress force deriving from the tightening of the two screws is obtained throughout the entire contact surface between the bar portions and respective support provided on the joint.
A structure of this type has the drawback that the assembly requires a long time of assembly time since the connection of each bar with the joint involves the tightening of two screws. Furthermore, this structure allows a small number of composition-resolution operations; in fact, the said threaded holes are obtained in an aluminum body, whose resistance to the wear is much lower than that of the steel of the screws and consequently, after some composition-resolution operations, the thread deteriorates so as to render the connection no longer reliable.